[app-server] feat: v2 apply_patch approval flow (openai#6760)

This PR adds the API V2 version of the apply_patch approval flow, which
centers around `ThreadItem::FileChange`.

This PR wires the new RPC (`item/fileChange/requestApproval`, V2 only)
and related events (`item/started`, `item/completed` for
`ThreadItem::FileChange`, which are emitted in both V1 and V2) through
the app-server
protocol. The new approval RPC is only sent when the user initiates a
turn with the new `turn/start` API so we don't break backwards
compatibility with VSCE.

Similar to openai#6758, the approach I
took was to make as few changes to the Codex core as possible,
leveraging existing `EventMsg` core events, and translating those in
app-server. I did have to add a few additional fields to
`EventMsg::PatchApplyBegin` and `EventMsg::PatchApplyEnd`, but those
were fairly lightweight.

However, the `EventMsg`s emitted by core are the following:
```
1) Auto-approved (no request for approval)

- EventMsg::PatchApplyBegin
- EventMsg::PatchApplyEnd

2) Approved by user
- EventMsg::ApplyPatchApprovalRequest
- EventMsg::PatchApplyBegin
- EventMsg::PatchApplyEnd

3) Declined by user
- EventMsg::ApplyPatchApprovalRequest
- EventMsg::PatchApplyBegin
- EventMsg::PatchApplyEnd
```

For a request triggering an approval, this would result in:
```
item/fileChange/requestApproval
item/started
item/completed
```

which is different from the `ThreadItem::CommandExecution` flow
introduced in openai#6758, which does the
below and is preferable:
```
item/started
item/commandExecution/requestApproval
item/completed
```

To fix this, we leverage `TurnSummaryStore` on codex_message_processor
to store a little bit of state, allowing us to fire `item/started` and
`item/fileChange/requestApproval` whenever we receive the underlying
`EventMsg::ApplyPatchApprovalRequest`, and no-oping when we receive the
`EventMsg::PatchApplyBegin` later.

This is much less invasive than modifying the order of EventMsg within
core (I tried).

The resulting payloads:
```
{
  "method": "item/started",
  "params": {
    "item": {
      "changes": [
        {
          "diff": "Hello from Codex!\n",
          "kind": "add",
          "path": "/Users/owen/repos/codex/codex-rs/APPROVAL_DEMO.txt"
        }
      ],
      "id": "call_Nxnwj7B3YXigfV6Mwh03d686",
      "status": "inProgress",
      "type": "fileChange"
    }
  }
}
```

```
{
  "id": 0,
  "method": "item/fileChange/requestApproval",
  "params": {
    "grantRoot": null,
    "itemId": "call_Nxnwj7B3YXigfV6Mwh03d686",
    "reason": null,
    "threadId": "019a9e11-8295-7883-a283-779e06502c6f",
    "turnId": "1"
  }
}
```

```
{
  "id": 0,
  "result": {
    "decision": "accept"
  }
}
```

```
{
  "method": "item/completed",
  "params": {
    "item": {
      "changes": [
        {
          "diff": "Hello from Codex!\n",
          "kind": "add",
          "path": "/Users/owen/repos/codex/codex-rs/APPROVAL_DEMO.txt"
        }
      ],
      "id": "call_Nxnwj7B3YXigfV6Mwh03d686",
      "status": "completed",
      "type": "fileChange"
    }
  }
}
```

Author: owenlin0

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -438,6 +438,13 @@ server_request_definitions! {
         response: v2::CommandExecutionRequestApprovalResponse,
     },
 
+    /// Sent when approval is requested for a specific file change.
+    /// This request is used for Turns started via turn/start.
+    FileChangeRequestApproval => "item/fileChange/requestApproval" {
+        params: v2::FileChangeRequestApprovalParams,
+        response: v2::FileChangeRequestApprovalResponse,
+    },
+
     /// DEPRECATED APIs below
     /// Request to approve a patch.
     /// This request is used for Turns started via the legacy APIs (i.e. SendUserTurn, SendUserMessage).

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -794,20 +794,23 @@ pub struct FileUpdateChange {
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
-#[serde(rename_all = "camelCase")]
+#[serde(tag = "type", rename_all = "camelCase")]
+#[ts(tag = "type")]
 #[ts(export_to = "v2/")]
 pub enum PatchChangeKind {
     Add,
     Delete,
-    Update,
+    Update { move_path: Option<PathBuf> },
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]
 pub enum PatchApplyStatus {
+    InProgress,
     Completed,
     Failed,
+    Declined,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
@@ -982,6 +985,26 @@ pub struct CommandExecutionRequestApprovalResponse {
     pub accept_settings: Option<CommandExecutionRequestAcceptSettings>,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct FileChangeRequestApprovalParams {
+    pub thread_id: String,
+    pub turn_id: String,
+    pub item_id: String,
+    /// Optional explanatory reason (e.g. request for extra write access).
+    pub reason: Option<String>,
+    /// [UNSTABLE] When set, the agent is asking the user to allow writes under this root
+    /// for the remainder of the session (unclear if this is honored today).
+    pub grant_root: Option<PathBuf>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[ts(export_to = "v2/")]
+pub struct FileChangeRequestApprovalResponse {
+    pub decision: ApprovalDecision,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]

codex-rs/app-server-test-client/src/main.rs

@@ -24,6 +24,8 @@ use codex_app_server_protocol::ClientRequest;
 use codex_app_server_protocol::CommandExecutionRequestAcceptSettings;
 use codex_app_server_protocol::CommandExecutionRequestApprovalParams;
 use codex_app_server_protocol::CommandExecutionRequestApprovalResponse;
+use codex_app_server_protocol::FileChangeRequestApprovalParams;
+use codex_app_server_protocol::FileChangeRequestApprovalResponse;
 use codex_app_server_protocol::GetAccountRateLimitsResponse;
 use codex_app_server_protocol::InitializeParams;
 use codex_app_server_protocol::InitializeResponse;
@@ -677,6 +679,9 @@ impl CodexClient {
             ServerRequest::CommandExecutionRequestApproval { request_id, params } => {
                 self.handle_command_execution_request_approval(request_id, params)?;
             }
+            ServerRequest::FileChangeRequestApproval { request_id, params } => {
+                self.approve_file_change_request(request_id, params)?;
+            }
             other => {
                 bail!("received unsupported server request: {other:?}");
             }
@@ -717,6 +722,37 @@ impl CodexClient {
         Ok(())
     }
 
+    fn approve_file_change_request(
+        &mut self,
+        request_id: RequestId,
+        params: FileChangeRequestApprovalParams,
+    ) -> Result<()> {
+        let FileChangeRequestApprovalParams {
+            thread_id,
+            turn_id,
+            item_id,
+            reason,
+            grant_root,
+        } = params;
+
+        println!(
+            "\n< fileChange approval requested for thread {thread_id}, turn {turn_id}, item {item_id}"
+        );
+        if let Some(reason) = reason.as_deref() {
+            println!("< reason: {reason}");
+        }
+        if let Some(grant_root) = grant_root.as_deref() {
+            println!("< grant root: {}", grant_root.display());
+        }
+
+        let response = FileChangeRequestApprovalResponse {
+            decision: ApprovalDecision::Accept,
+        };
+        self.send_server_request_response(request_id, &response)?;
+        println!("< approved fileChange request for item {item_id}");
+        Ok(())
+    }
+
     fn send_server_request_response<T>(&mut self, request_id: RequestId, response: &T) -> Result<()>
     where
         T: Serialize,